Two-wheeled motor vehicle brake control method and system

ABSTRACT

To enable, with respect to a vehicle whose vehicle body is easily lifted to a relatively large extent even in a relatively early stage when rear wheel lifting is detected, more rapid and reliable securement of the safety of the vehicle body with respect to that rear wheel lifting. 
     When lifting of a rear wheel is detected, in contrast to what has conventionally been the case, pressure reduction of brake pressure of a front wheel is immediately started (S 100 , S 102 ) regardless of whether or not there is occurrence of skidding of the front wheel, a stepwise reduction of brake pressure is performed while lifting of the rear wheel is being detected, and when the integrated amount of that amount of pressure reduction reaches a predetermined value, pressure reduction is ended even in a state where rear wheel lifting is being detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a two-wheeled motor vehicle brakecontrol method and system and in particular to the rapid securement ofthe safety of a vehicle with respect to rear wheel lifting.

2. Description of the Related Art

Conventionally, it has been well known that, in two-wheeled motorvehicles, the larger the ratio between the height of the center ofgravity of the vehicle and the inter-axial distance between the frontand rear wheels is, the easier it is for the phenomenon of so-calledlifting of the rear wheel to occur. Additionally, various technologieshave been proposed with respect to such rear wheel lifting from thestandpoint of securing the safety of the vehicle and the rider, and atechnology that reduces brake pressure by a certain amount to therebysecure the safety of the vehicle when, for example, as disclosed inJapanese Patent No. 3,416,819, lifting of the rear wheel is detected andpredetermined skidding or greater is occurring in the front wheel ispublicly known.

However, it is not the case that the aforementioned conventionaltechnologies can always be applied regardless of differences in theconditions of the vehicle—that is, the weight of the vehicle body, thelength of the vehicle body, and the height of the vehicle—and dependingon differences in the conditions of the vehicle, there are also vehicleswhere a reduction of brake pressure becomes necessary beforepredetermined skidding or greater of the front wheel is detected.

SUMMARY OF THE INVENTION

Related application Ser. No. 12/161,367, filed Jul. 18, 2008, allowed;Ser. No. 12/162,220, filed Jul. 25, 2008, currently pending; Ser. No.12/162,223, filed Jul. 25, 2008, currently pending; and Ser. No.12/162,626, filed Jul. 30, 2008, currently pending, are directed tosimilar subject matter. The '367 application is directed to a brakecontrol method and system which provides improved controllability withrespect to rear wheel lifting; the '220 application is directed to abrake control method and system that can prevent a so-called no-brakestate; the '223 application is directed to a brake control method andsystem that can reliably control and prevent rear wheel lifting causedby an abrupt brake operation; and the '626 application is directed to atwo-wheeled motor vehicle brake control method and system for securementof high safety with respect to rear wheel lifting by reducing a pressureincrease gradient of a wheel cylinder pressure of the front wheelimmediately after rear wheel lifting.

The present invention has been made in view of the above-describedsituation and provides a brake control method and system which, withrespect to a vehicle where lifting of the vehicle body easily occurs toa relatively large extent even in a relatively early stage when rearwheel lifting is detected, enable more rapid and reliable securement ofsafety with respect to that rear wheel lifting.

According to a first aspect of the present invention, there is provideda two-wheeled motor vehicle brake control method comprising: immediatelystarting reduction of the brake pressure of a front wheel when liftingof a rear wheel is detected, performing, in a stepwise manner, reductionof that brake pressure while lifting of the rear wheel is beingdetected, and, when an integrated amount of stepwise pressure reductionreaches a predetermined value, ending pressure reduction even in a statewhere rear wheel lifting is being detected.

According to a second aspect of the present invention, there is provideda two-wheeled motor vehicle brake control method comprising: immediatelyreducing the brake pressure of a front wheel by a certain amount whenlifting of a rear wheel is detected, and next performing pressureincrease of an amount that is different from the amount of pressurereduction.

According to a third aspect of the present invention, there is provideda two-wheeled motor vehicle brake control system configured to becapable of transmitting oil pressure arising in a front brake mastercylinder in response to operation of a first brake operator to a frontwheel cylinder via an oil pressure system, capable of transmitting oilpressure arising in a rear brake master cylinder in response tooperation of a second brake operator to a rear wheel cylinder via an oilpressure system, capable of discharging brake fluid of the front wheelcylinder to a front reservoir as desired, and capable of detectingwhether or not there is lifting of a rear wheel, wherein the brakecontrol system is configured to immediately start reduction of the brakepressure of the front wheel when lifting of the rear wheel is detected,perform, in a stepwise manner, reduction of the brake pressure of thefront wheel while lifting of the rear wheel is being detected, and, whenan integrated amount of stepwise pressure reduction reaches apredetermined value, end pressure reduction even in a state where rearwheel lifting is being detected.

According to a fourth aspect of the present invention, there is provideda two-wheeled motor vehicle brake control system configured to becapable of transmitting oil pressure arising in a front brake mastercylinder in response to operation of a first brake operator to a frontwheel cylinder via an oil pressure system, capable of transmitting oilpressure arising in a rear brake master cylinder in response tooperation of a second brake operator to a rear wheel cylinder via an oilpressure system, capable of discharging brake fluid of the front wheelcylinder to a front reservoir as desired, and capable of detectingwhether or not there is lifting of a rear wheel, wherein the brakecontrol system is configured to immediately reduce the brake pressure ofa front wheel by a predetermined pressure when lifting of the rear wheelis detected, and next perform pressure increase of an amount that isdifferent from the amount of pressure reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configural diagram showing an example of the configurationof a two-wheeled motor vehicle brake control system in an embodiment ofthe present invention;

FIG. 2 is a sub-routine flowchart showing a control procedure in a firstexample of brake control processing that is executed by an electroniccontrol unit used in the two-wheeled motor vehicle brake control systemshown in FIG. 1;

FIG. 3 is a sub-routine flowchart showing a control procedure in asecond example of brake control processing that is executed by theelectronic control unit used in the two-wheeled motor vehicle brakecontrol system shown in FIG. 1;

FIG. 4 is a sub-routine flowchart showing a control procedure in a thirdexample of brake control processing that is executed by the electroniccontrol unit used in the two-wheeled motor vehicle brake control systemshown in FIG. 1;

FIG. 5 is a general characteristic line diagrams for describing therelationship between a change in brake pressure obtained by a frontwheel cylinder and a rear wheel lifting detection signal in the thirdexample whose control procedure is shown in FIG. 4, with FIG. 5(A) beinga general characteristic line diagram generally showing an example of achange in brake pressure obtained by the front wheel cylinder and FIG.5(B) being a general waveform diagram generally showing an example of achange in the rear wheel lifting detection signal;

FIG. 6 is a sub-routine flowchart showing a control procedure in afourth example of brake control processing that is executed by theelectronic control unit used in the two-wheeled motor vehicle brakecontrol system shown in FIG. 1;

FIG. 7 is a sub-routine flowchart showing a control procedure in a fifthexample of brake control processing that is executed by the electroniccontrol unit used in the two-wheeled motor vehicle brake control systemshown in FIG. 1;

FIG. 8 is a sub-routine flowchart showing a control procedure in a sixthexample of brake control processing that is executed by the electroniccontrol unit used in the two-wheeled motor vehicle brake control systemshown in FIG. 1; and

FIG. 9 is a general characteristic line diagrams for describing therelationship between a change in brake pressure obtained by the frontwheel cylinder and the rear wheel lifting detection signal in the sixthexample whose control procedure is shown in FIG. 8, with FIG. 9(A) beinga general characteristic line diagram generally showing an example of achange in brake pressure obtained by the front wheel cylinder and FIG.9(B) being a general waveform diagram generally showing an example of achange in the rear wheel lifting detection signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, an embodiment of the present invention will be described withreference to FIG. 1 to FIG. 9.

It will be noted that the members and arrangements described below arenot intended to limit the invention and can be variously modified withinthe scope of the gist of the invention.

First, an example of the configuration of a two-wheeled motor vehiclebrake control system in the embodiment of the invention will bedescribed with reference to FIG. 1.

This brake control system S is broadly divided into a front brake mastercylinder 1 that is disposed so as to be capable of converting theoperational force of a brake handle 35 serving as a first brake operatorinto oil pressure, a rear brake master cylinder 2 that is disposed so asto be capable of converting the operational force of a brake pedal 36serving as a second brake operator into oil pressure, a front wheelcylinder 3 that imparts brake force to a front wheel 37 in response tothe oil pressure from the front brake master cylinder 1, a rear wheelcylinder 4 that imparts brake force to a rear wheel 38 in response tothe oil pressure from the rear brake master cylinder 2, and an antilockbrake control system 101 that is disposed between the front and rearbrake master cylinders 1 and 2 and the front and rear wheel cylinders 3and 4.

The front brake master cylinder 1 and the front wheel cylinder 3 areinterconnected by a first main oil pressure tube 5, and a front main oilpressure tube-use throttle 6 and a first electromagnetic valve 7 that isordinarily in an opened state are disposed in order from the front brakemaster cylinder 1 side midway along the first main oil pressure tube 5.Moreover, a front main oil pressure tube-use check valve 8 is disposedso as to bypass the front main oil pressure tube-use throttle 6 and thefirst electromagnetic valve 7 and in a direction where it deters thereverse flow of brake oil (brake fluid) from the front wheel cylinder 3to the front brake master cylinder 1.

Similarly, the rear brake master cylinder 2 and the rear wheel cylinder4 are interconnected by a second main oil pressure tube 9, and a rearmain oil pressure tube-use throttle 10 and a second electromagneticvalve 11 that is ordinarily in an opened state are disposed in orderfrom the rear brake master cylinder 2 side midway along the second mainoil pressure tube 9. Moreover, a rear main oil pressure tube-use checkvalve 12 is disposed so as to bypass the rear main oil pressure tube-usethrottle 10 and the second electromagnetic valve 11 and in a directionwhere it deters the reverse flow of brake oil from the rear wheelcylinder 4 to the rear brake master cylinder 2.

Further, a front reservoir connection-use oil pressure tube 13 isconnected to an appropriate position of the first main oil pressure tube5 between the first electromagnetic valve 7 and the front wheel cylinder3, a front reservoir-use throttle 14 and a front reservoir inflowcontrol-use electromagnetic valve 15 are disposed in order from thefront wheel cylinder 3 side midway along the front reservoirconnection-use oil pressure tube 13, and a front reservoir 16 isconnected via these. Here, the front reservoir inflow control-useelectromagnetic valve 15 is ordinarily in a closed state.

Moreover, a front return-use oil pressure tube 17 that is communicatedwith the front brake master cylinder 1 is connected to the frontreservoir connection-use oil pressure tube 13 at an appropriate positionbetween the front reservoir inflow control-use electromagnetic valve 15and the front reservoir 16, and a front return path-use throttle 18, afirst front return path-use check valve 19 and a second front returnpath-use check valve 20 are disposed in order from the front brakemaster cylinder 1 side midway along the front return-use oil pressuretube 17.

Further, basically similar to the configuration of the aforementionedfirst main oil pressure tube 5, a rear reservoir connection-use oilpressure tube 21 is connected to an appropriate position of the secondmain oil pressure tube 9 between the second electromagnetic valve 11 andthe rear wheel cylinder 4, a rear reservoir-use throttle 22 and a rearreservoir inflow control-use electromagnetic valve 23 are disposed inorder from the rear wheel cylinder 4 side midway along the rearreservoir connection-use oil pressure tube 21, and a rear reservoir 24is connected via these. Here, the rear reservoir inflow control-useelectromagnetic valve 23 is ordinarily in a closed state.

Moreover, a rear return-use oil pressure tube 25 that is communicatedwith the rear brake master cylinder 2 is connected to the rear reservoirconnection-use oil pressure tube 21 at an appropriate position betweenthe rear reservoir inflow control-use electromagnetic valve 23 and therear reservoir 24, and a rear return path-use throttle 26, a first rearreturn path-use check valve 27 and a second rear return path-use checkvalve 28 are disposed in order from the rear brake master cylinder 2side midway along the front return-use oil pressure tube 25.

Moreover, an oil pressure pump device 31 that is shared between thefront brake and the rear brake is disposed in the antilock brake controlsystem 101. That is, the oil pressure pump device 31 is generallyconfigured by a motor 32 and two plungers 33 a and 33 b that arereciprocally moved by an unillustrated fixed cam that is fixedlyattached to an output shaft (not shown) of the motor 32.

Additionally, the one plunger 33 a is connected between the first frontreturn path-use check valve 19 and the second front return path-usecheck valve 20, the other plunger 33 b is connected between the firstrear return path-use check valve 27 and the second rear return path-usecheck valve 28, the brake oil of the front reservoir 16 is sucked up andrefluxed to the front brake master cylinder 1 and the brake oil of therear reservoir 24 is sucked up and refluxed to the rear brake mastercylinder 2 by the reciprocating motion of the plungers 33 a and 33 b.

Control of the operation of each of the first and second electromagneticvalves 7 and 11, the front reservoir inflow control-use electromagneticvalve 15, the rear reservoir inflow control-use electromagnetic valve 23and the motor 32 is performed by an electronic control unit (notated as“ECU” in FIG. 1) 51.

The electronic control unit 51 is configured to be disposed with amicrocomputer (not shown) that has a publicly known/commonly knownconfiguration and memory elements (not shown) such as a RAM and a ROM.

The electronic control unit 51 executes various control programs forcontrolling the traveling of the vehicle that are stored in theunillustrated memory elements and performs various operation controlsnecessary for the driving and traveling of the vehicle. Examples of suchoperational controls of the vehicle include engine control, ABS control(Antilock Brake System), processing to monitor the wheel velocities fordetermining whether or not there is an abnormality in wheel velocitysensors, and processing to detect rear wheel lifting. Moreover, in theembodiment of the present invention, later-described brake controlprocessing is executed.

In order to performed the aforementioned control processing, detectionsignals of wheel velocity sensors 45 and 46 that are correspondinglydisposed in order to detect the wheel velocities of the front wheel 37and the rear wheel 38, a detection signal of a first pressure sensor 47that detects the generated pressure of the front brake master cylinder 1and a detection signal of a second pressure sensor 48 that detects thegenerated pressure of the front wheel cylinder 3 are inputted to theelectronic control unit 51.

Moreover, detection signals of a brake lever actuation switch (notshown) that detects actuation of the brake handle 35 and a brake pedalactuation switch (not shown) that detects actuation of the brake pedal36 are also inputted to the electronic control unit 51.

Further, a motor drive circuit 41 that generates and outputs a drivesignal with respect to the motor 32 in response to a control signal fromthe electronic control unit 51 is disposed.

Moreover, an electromagnetic valve drive circuit 42 that controls thedriving of the first and second electromagnetic valves 7 and 11, thefront reservoir inflow control-use electromagnetic valve 15 and the rearreservoir inflow control-use electromagnetic valve 23 in response tocontrol signals from the electronic control unit 51 is disposed. It willbe noted that, in FIG. 1, the connections between the electromagneticvalve drive circuit 42 and the respective electromagnetic valves areomitted in order to simplify the drawing and make the drawing easier tounderstand.

It will be noted that the basic operation of the brake control system Sof the aforementioned configuration is the same as that of this type ofpublicly known/commonly known brake control system, so detaileddescription here will be omitted, but the overall operation will begenerally described.

For example, when the brake handle 35 is operated in order to cause thebrake to act, a predetermined detection signal corresponding to the factthat that operation has been detected by the brake lever actuationswitch (not shown) that detects operation of the brake handle 35 isinputted to the electronic control unit 51. At the same time, brakefluid of an oil pressure corresponding to operation of the brake handle35 is supplied from the brake master cylinder 1 to the front wheelcylinder 3, brake force is generated, and the brake force acts on thefront wheel 37.

Then, in the electronic control unit 51, when it is judged that antilockbrake control is necessary, the first electromagnetic valve 7 isexcited, the first main oil pressure tube 5 is placed in anon-communicated state, and the oil pressure of the front wheel cylinder3 is held at a constant. Then, in the electronic control unit 51, whenit is judged that the brake should be eased, the front reservoir inflowcontrol-use electromagnetic valve 15 is excited. As a result, the brakefluid of the front wheel cylinder 3 is discharged to the front reservoir16 via the front reservoir inflow control-use electromagnetic valve 15,and the brake is eased.

At the same time, the motor 32 is driven by the electronic control unit51 via the motor drive circuit 41, and the brake fluid stored in thefront reservoir 16 is sucked up by the motion of the plunger 33 a andrefluxed to the front brake master cylinder 1.

It will be noted that when the brake pedal 36 is operated also, brakeforce with respect to the wheel 38 is obtained in basically the samemanner as in the case of the brake handle 35 aforementioned, andalleviation of the brake force is performed, so description here will beomitted.

Next, a first example of brake control processing that is executed bythe aforementioned electronic control unit 51 in this configuration willbe described with reference to the sub-routine flowchart shown in FIG.2.

When processing is started, it is determined whether or not rear wheellifting has occurred (refer to step S100 of FIG. 2). Here, it is assumedthat the two-wheeled motor vehicle to which this brake controlprocessing is applied includes a rear wheel lifting detection function.That is, a program for rear wheel lifting detection is executed by theelectronic control unit 51, and when it is determined that rear wheellifting has occurred, then a detection signal is generated inside theelectronic control unit 51. It is not necessary for this rear wheellifting detection processing to be specific to the invention of thepresent application and it may be publicly known rear wheel liftingdetection processing. That is, as this rear wheel lifting detectionmethod, for example, the method (JP-A-2002-29403) pertaining to theproposal of the applicant of the present application, which calculates apseudo vehicle body velocity on the basis of wheel velocity and judgesrear wheel lifting by the magnitude of a pseudo vehicle bodydeceleration calculated from that pseudo vehicle body velocity, issuitable.

Consequently, as for the determination of whether or not there isoccurrence of lifting in step S100, similarly determining whether or nota detection signal has been generated which indicates that rear wheellifting has occurred in the aforementioned rear wheel lifting detectionprocessing that is executed by an unillustrated main routine issuitable.

Then, when it is determined that rear wheel lifting is not occurring (inthe case of NO), then processing is immediately ended. On the otherhand, when it is determined that rear wheel lifting has occurred (in thecase of YES), then the pressure of the front wheel cylinder 3 is reducedby a certain amount (refer to step S102 of FIG. 2) and the sub-routinereturns to the unillustrated main routine.

That is, the front reservoir inflow control-use electromagnetic valve 15is placed in an opened state by the electronic control unit 51 via theelectromagnetic valve drive circuit 42, and the brake fluid of the frontwheel cylinder 3 is discharged to the front reservoir 16. Then, when itis determined in the electronic control unit 51 on the basis of thedetection signal from the second pressure sensor 48 that the pressure ofthe front wheel cylinder 3 has dropped to a predetermined pressure, thefront reservoir inflow control-use electromagnetic valve 15 is placed ina closed state via the electromagnetic drive circuit 42, and thesub-routine returns to a state where normal brake control is performed.

It will be noted that, because the appropriate value for the amount ofpressure reduction will differ depending on the conditions of thevehicle—that is, the weight of the vehicle body, the length of thevehicle body, and the height of the vehicle—it is suitable to select anappropriate value on the basis of simulations and experiments.

In this first control processing example, in contrast to what hasconventionally been the case where rear wheel lifting is detected,predetermined skidding or greater of the front wheel is detected andbrake pressure is reduced, when rear wheel lifting is detected, thefront wheel cylinder 3 is reduced by a certain amount, that is, in otherwords, the brake pressure is reduced by a certain amount, so in avehicle that easily falls into a considerable rear wheel lifting statealready at the point in time when rear wheel lifting is detected,control of the rear wheel lifting is performed rapidly in comparison towhat has conventionally been the case, and the safety of the vehiclebecomes rapid and reliable.

Next, a second example of brake control processing will be describedwith reference to FIG. 3. It will be noted that the same numbers will begiven to steps having the same processing content as those of the stepsshown in FIG. 2, detailed description of those steps having the sameprocessing content will be omitted, and the points that are differentwill be mainly described below.

This second example is an example configured such that, when rear wheellifting is detected, the amount of pressure reduction of the front wheelcylinder 3 is changed in response to that lifting.

That is, in the determination processing of step S100, when it isdetermined that rear wheel lifting has occurred, an amount of pressurereduction corresponding to that lifting is computed and calculated(refer to step S101 of FIG. 3). Specifically, first, lifting in thephenomenon of rear wheel lifting caused by a sudden brake operationtends to be substantially proportional to the magnitude of vehicle bodydeceleration or the magnitude of the amount of pressure increase in thefront wheel cylinder 3.

Consequently, the magnitude of the amount of change in vehicle bodydeceleration or the amount of pressure increase in the front wheelcylinder 3 can be used as a predetermined parameter that becomes anindex of lifting of the rear wheel. Thus, it is suitable to determine inadvance, by simulations and experiments, an appropriate amount ofpressure reduction of the front wheel cylinder 3 with respect to themagnitude of the amount of change in vehicle body deceleration or theamount of pressure increase in the front wheel cylinder 3, map orexpress as an arithmetic expression an appropriate amount of pressurereduction of the front wheel cylinder 3 with respect to the magnitude ofvarious amounts of change in vehicle body deceleration or variousamounts of pressure increase in the front wheel cylinder 3 on the basisof this, and use this in step S101. That is, one method of pressurereduction amount calculation is a method that computes and calculates,by the aforementioned map or arithmetic expression, an appropriateamount of pressure reduction of the front wheel cylinder 3 with respectto the amount of change in vehicle body deceleration at this point intime.

Further, another method of pressure reduction amount calculation is amethod that computes and calculates, by the aforementioned map orarithmetic expression, an appropriate amount of pressure reduction ofthe front wheel cylinder 3 with respect to the magnitude of the pressureincrease of the front wheel cylinder 3.

Moreover, vehicle body deceleration, brake pressure, or in other wordsthe front wheel cylinder 3 pressure, can also become an index of liftingof the rear wheel. Additionally, when these are used as an index,similar to what has been mentioned before, it is suitable to ensure thatan appropriate amount of pressure reduction of the front wheel cylinder3 corresponding to vehicle body deceleration or the front wheel cylinderpressure can be calculated by the map or arithmetic expression that hasbeen obtained on the basis of simulations or the like.

Then, pressure reduction of the front wheel cylinder 3 by the amount ofpressure reduction that has been calculated as mentioned above isperformed.

It will be noted that vehicle body deceleration, which is apredetermined parameter that becomes an index of lifting of the rearwheel, is determined as being equal to (V1−V2)/Δt assuming that V1represents a vehicle body velocity at a given time t1 and that V2represents a vehicle body velocity at a time t2 after the elapse of aderivative time Δt from time t1. Further, the amount of change invehicle body deceleration is determined as being equal to (a1−a2)Δtassuming that a1 represents vehicle body deceleration at a given time t1and that a2 represents vehicle body deceleration at a time t2 after theelapse of a derivative time Δt from time t1. Additionally, the vehiclebody velocity is determined by a publicly known predetermined arithmeticexpression on the basis of the wheel velocity sensors 45 and 46.

Moreover, the pressure of the front wheel cylinder 3 is a pressure p(t0)of the front wheel cylinder 3 at a given time t0, and the magnitude ofthe pressure increase thereof is determined as {p(t0+Δt)−p(t0)}/Δtassuming that p(t0) represents the pressure of the front wheel cylinder3 at a given time t0 and that p(t0+Δt) represents the pressure of thefront wheel cylinder 3 at a point in time after the elapse of aderivative time Δt from that.

Next, a third example of brake control processing will be described withreference to FIG. 4 and FIG. 5. It will be noted that the same numberswill be given to steps having the same processing content as those ofthe steps shown in FIG. 2, detailed description of those steps havingthe same processing content will be omitted, and the points that aredifferent will be mainly described below.

This third example is an example configured to repeat, in a stepwisemanner, a predetermined amount of pressure reduction of the front wheelcylinder 3 while rear wheel lifting is being detected.

That is, in the determination processing of step S100, when it isdetermined that rear wheel lifting has occurred, then the pressure ofthe front wheel cylinder 3 is reduced by a certain amount (refer to stepS102 of FIG. 4), and next it is determined whether or not rear wheellifting still continues to be detected (refer to step S104 of FIG. 4).

Then, in step S104, when it is determined that rear wheel lifting stillcontinues to be detected (in the case of YES), then the sub-routinereturns to the processing of the previous step S102 and the pressure ofthe front wheel cylinder 3 is again reduced by a certain amount, andwhen it is determined that rear wheel lifting is no longer detected (inthe case of NO), then the series of processing is ended, and thesub-routine returns to the unillustrated main routine and returns to anormal brake control state.

In FIG. 5, there are shown general characteristic line diagrams where achange in brake pressure and a change in the rear wheel liftingdetection signal in this third brake control processing are generallyshown, and the same drawing will be described below.

FIG. 5(A) is a general characteristic line diagram generally showing anexample of a change in brake pressure obtained by the front wheelcylinder 3, and FIG. 5(B) is a general characteristic line diagramgenerally showing an example of a change in the detection signal that isgenerated when it is determined inside the electronic control unit 51that there is rear wheel lifting.

In FIG. 5(A), the rise in brake pressure until time t1 corresponds to asituation where a sudden brake operation of the brake handle 35 has beenperformed. Additionally, a state is shown in FIG. 5(B) where, because ofthis sudden rise in brake pressure, at time t1, when it is determined bythe electronic control unit 51 that there is rear wheel lifting, thedetection signal is outputted as a logical value “High” in responsethereto.

Then, at time t1, rear wheel lifting is detected, whereby pressurereduction of a predetermined pressure of the front wheel cylinder 3 isperformed as mentioned previously, and brake pressure falls to apredetermined pressure in correspondence thereto (refer to the point intime of time t1 of FIG. 5(A)). A state is shown in FIG. 5(A) where, fromthen on, at time t2, brake pressure is reduced every predeterminedpressure in a stepwise manner until rear wheel lifting is no longerdetected (refer to FIG. 5(B)).

Next, a fourth example of brake control processing will be describedwith reference to FIG. 6. It will be noted that the same numbers will begiven to steps having the same processing content as those of the stepsshown in FIG. 2 or FIG. 4, detailed description of those steps havingthe same processing content will be omitted, and the points that aredifferent will be mainly described below.

This fourth example is an example where, when a predetermined amount ofpressure reduction of the front wheel cylinder 3 is repeated in astepwise manner while rear wheel lifting is being detected, a limit isdisposed on the number of times of that pressure reduction.

That is, in step S104, when it is determined that rear wheel lifting isnot being detected (in the case of NO), then the series of processing isended. On the other hand, in step S104, when it is determined that rearwheel lifting still continues to be detected (in the case of YES), thenit is determined whether or not pressure reduction of a predeterminednumber of times has been performed (refer to step S106 of FIG. 6), andwhen it is determined that pressure reduction has not reached thepredetermined number of times (in the case of NO), then the sub-routinereturns to the processing of step S102 and the series of processing isrepeated. Further, in step S106, when it is determined that pressurereduction of the predetermined number of times has been performed (inthe case of YES), then the series of processing is ended, and thesub-routine returns to the unillustrated main routine and returns to anormal brake control state.

In this manner, by disposing a limit on the number of times of pressurereduction, a situation that results in a so-called no-brake state isprevented.

Next, a fifth example of brake control processing will be described withreference to FIG. 7. It will be noted that the same numbers will begiven to steps having the same processing content as those of the stepsshown in FIG. 2 or FIG. 6, detailed description of those steps havingthe same processing content will be omitted, and the points that aredifferent will be mainly described below.

This fifth example is an example where, when a predetermined amount ofpressure reduction of the front wheel cylinder 3 is repeated in astepwise manner while rear wheel lifting is being detected, a limit isdisposed on the total pressure reduction amount.

That is, in step S104, when it is determined that rear wheel lifting isnot being detected (in the case of NO), then the series of processing isended. On the other hand, in step S104, when it is determined that rearwheel lifting still continues to be detected (in the case of YES), thenit is determined whether or not the total pressure reduction amount hasreached a predetermined value (refer to step S107 of FIG. 7), and whenthe total pressure reduction amount has not reached the predeterminedvalue (in the case of NO), then the sub-routine returns to theprocessing of step S102 and the series of processing is repeated. Here,“total pressure reduction amount” refers to an integrated value of theamount of pressure reduction performed by repeating the pressurereduction of step S102.

Further, in step S107, when it is determined that the total pressurereduction amount has reached the predetermined value (in the case ofYES), then the series of processing is ended, and the sub-routinereturns to the unillustrated main routine and returns to a normal brakecontrol state.

In this manner, by disposing a limit on the total pressure reductionamount, a situation that results in a so-called no-brake state isprevented.

Next, a sixth example of brake control processing will be described withreference to FIG. 8 and FIG. 9. It will be noted that the same numberswill be given to steps having the same processing content as those ofthe steps shown in FIG. 2, detailed description of those steps havingthe same processing content will be omitted, and the points that aredifferent will be mainly described below.

This sixth example is an example where, after a predetermined amount ofpressure reduction of the front wheel cylinder 3 has been performed, thepressure of the front wheel cylinder 3 is increased a little.

That is, in step S102, after a predetermined amount of pressurereduction of the front wheel cylinder 3 has been performed, the pressureof the front wheel cylinder 3 is increase by a predetermined amountafter the elapse of an appropriate amount of time, and the series ofprocessing is ended (refer to step S104A of FIG. 8). This brake controlis control which, in a vehicle where the brake force of the vehicle bodyends up dropping to a relatively large degree because of a reduction inbrake pressure of the front wheel caused by the lightness in weight ofthe vehicle body, for example, and which tends to easily fall into atraveling state, enables a situation where the vehicle falls into such astate to be controlled and avoided by an increase in brake pressure tothe front wheel.

In FIG. 9, there are shown general characteristic line diagrams where achange in brake pressure and a change in the rear wheel liftingdetection signal in this sixth brake control processing are generallyshown, and the same drawing will be described below.

FIG. 9(A) is a general characteristic line diagram generally showing anexample of a change in brake pressure obtained by the front wheelcylinder 3, and FIG. 9(B) is a general characteristic line diagramgenerally showing an example of a change in the detection signal that isgenerated when it is determined inside the electronic control unit 51that there is rear wheel lifting.

In FIG. 9(A), the rise in brake pressure until time t1 corresponds to asituation where a sudden brake operation of the brake handle 35 has beenperformed. Additionally, a state is shown in FIG. 9(B) where, because ofthis sudden rise in brake pressure, at time t1, when it is determined bythe electronic control unit 51 that there is rear wheel lifting, thedetection signal is outputted as a logical value “High” in responsethereto.

Then, at time t1, rear wheel lifting is detected, whereby pressurereduction of a predetermined pressure of the front wheel cylinder 3 isperformed as mentioned previously, and brake pressure falls to apredetermined pressure in correspondence thereto (refer to the point intime of time t1 of FIG. 9(A)).

Next, in accompaniment with an increase of a predetermined pressure ofthe front wheel cylinder 3 being performed, brake pressure is increasedby a magnitude corresponding to the amount of pressure increase (referto FIG. 9(A)).

It will be noted that, as for the time interval after reduction of apredetermined pressure of the front wheel cylinder 3 has been performed(refer to step S102 of FIG. 8) to until increase of a predeterminedpressure of the front wheel cylinder 3 is performed (refer to step S104Aof FIG. 8) and the amount of pressure increase and the like, it issuitable to select appropriate values on the basis of simulations andexperiments because appropriate values will differ depending ondifferences in the conditions of the vehicle—that is, the weight of thevehicle body, the length of the vehicle body, and the height of thevehicle.

The present invention can be applied to brake control of a two-wheeledmotor vehicle and is particularly suited for the realization of atwo-wheeled motor vehicle where there are desired avoidance of theoccurrence of a no-brake state resulting from excessive brake controland appropriate brake control while performing securement of brake forcewith respect to the vehicle body.

According to the present invention, when rear wheel lifting is detected,in contrary to what has conventionally been the case, the brake pressureof the front wheel is immediately reduced regardless of whether or notthere is occurrence of skidding of the front wheel, so lifting of theentire vehicle body can be rapidly and accurately controlled andprevented particularly in a vehicle whose entire vehicle body is easilylifted even by slight rear wheel lifting, and safety resulting fromsecurement of the safety of the vehicle and the rider can be improved.

Further, when the invention is configured such that reduction of thebrake pressure is performed in a stepwise manner and a limit is disposedon the number of times of that pressure reduction and the total pressurereduction amount, a situation that results in a so-called no brake statecan be prevented, and a vehicle whose safety and reliability are highercan be provided.

Moreover, when the invention is configured such that the brake pressureis reduced and thereafter slightly increased, safety and reliability canbe improved even more particularly in a vehicle that tends to easilylose brake force because of a reduction of the brake pressure.

1. A two-wheeled motor vehicle brake control system configured to becapable of transmitting oil pressure arising in a front brake mastercylinder in response to operation of a first brake operator to a frontwheel cylinder via an oil pressure system, capable of transmitting oilpressure arising in a rear brake master cylinder in response tooperation of a second brake operator to a rear wheel cylinder via an oilpressure system, capable of discharging brake fluid of the front wheelcylinder to a front reservoir as desired, and capable of detectingwhether or not there is lifting of a rear wheel, wherein the brakecontrol system is configured to immediately reduce the brake pressure ofa front wheel by a predetermined pressure when lifting of the rear wheelis detected, and next perform pressure increase of the front wheel,while lifting is being detected, by an amount that is different from theamount of pressure reduction.
 2. The two-wheeled motor vehicle brakecontrol system as recited in claim 1, wherein the pressure increase ofthe front wheel is by an amount that is less than the amount of pressurereduction.
 3. A two-wheeled motor vehicle brake control methodcomprising: transmitting oil pressure arising in a front brake mastercylinder in response to operation of a first brake operator to a frontwheel cylinder via an oil pressure system, transmitting oil pressurearising in a rear brake master cylinder in response to operation of asecond brake operator to a rear wheel cylinder via an oil pressuresystem, discharging brake fluid of the front wheel cylinder to a frontreservoir as desired, detecting whether or not there is lifting of arear wheel, immediately reducing the brake pressure of a front wheel bya predetermined pressure when lifting of the rear wheel is detected, andincreasing brake pressure of the front wheel, while lifting is beingdetected, by an amount that is different from the amount of pressurereduction.
 4. The two-wheeled motor vehicle brake control method asrecited in claim 3, wherein the pressure increase of the front wheel isby an amount that is less than the amount of pressure reduction.
 5. Atwo-wheeled motor vehicle brake control system configured to be capableof transmitting oil pressure arising in a front brake master cylinder inresponse to operation of a first brake operator to a front wheelcylinder via an oil pressure system, capable of transmitting oilpressure arising in a rear brake master cylinder in response tooperation of a second brake operator to a rear wheel cylinder via an oilpressure system, capable of discharging brake fluid of the front wheelcylinder to a front reservoir as desired, and capable of detectingwhether or not there is lifting of a rear wheel, wherein the brakecontrol system is configured to immediately start reduction of the brakepressure of the front wheel when lifting of the rear wheel is detected,perform, in a stepwise manner, reduction of the brake pressure of thefront wheel while lifting of the rear wheel is being detected and, whenan integrated amount of stepwise pressure reduction reaches apredetermined value, end pressure reduction even in a state where rearwheel lifting is being detected.
 6. A two-wheeled motor vehicle brakecontrol method comprising: transmitting oil pressure arising in a frontbrake master cylinder in response to operation of a first brake operatorto a front wheel cylinder via an oil pressure system, transmitting oilpressure arising in a rear brake master cylinder in response tooperation of a second brake operator to a rear wheel cylinder via an oilpressure system, discharging brake fluid of the front wheel cylinder toa front reservoir as desired, and detecting whether or not there islifting of a rear wheel, immediately starting reduction of the brakepressure of the front wheel when lifting of the rear wheel is detected,reducing the brake pressure of the front wheel in a stepwise mannerwhile lifting of the rear wheel is being detected and, when anintegrated amount of stepwise pressure reduction reaches a predeterminedvalue, ending pressure reduction even in a state where rear wheellifting is being detected.